can be obtained only with less-volatile paraffins, since highvolatile paraffins will vaporize from ultrafine particles within milliseconds due to the Kelvin effect (16). A solution to this problem may be the application of a heated (ca. 323 K) thermodenuder in front of the photoelectric aerosol sensor, which will remove not only high-volatile paraffins but also other interfering products (8).
CONCLUSIONSThe presented investigations have shown that an additivity of the photoelectric signals is given only for small PAH coverages on particles. In real exhaust situations similar PAH concentrations exist while the particle concentrations are substantially larger at least by a factor 1000; hence only low PAH surface coverages will result from real combustion processes except for residential wood combustion. Under these circumstances the photoelectric signal is likely to represent the sum of the single signals of all adsorbed PAHs. Analyzing cigarette smoke aerosols with the photoelectric aerosol sensor (A = 185 nm) and parallel wet-chemical techniques have confirmed the strong correlation between photoelectric signal and adsorbed PAH amounts (17). Also the applicability of this sensor as on-line and in situ detector for the measurement of PAHs in exhaust gases from waste combustion has been tested (18). Experiments with paraffin coatings have confirmed that aerosol photoemission only probes the surface composition of an aerosol system.
LITERATURE CITEDLevsen, K. Fresenius' J. Anal. Chem. 1988, 333, 467-478. Partrklge, P. A.; Shah, F. J.; Cernansky, N. P.; Suffet, I. H. Envhon. Sci. Techno/. 1987, 27, 403-408. Davis, C. S.; Fellin, P.; Otson, R. Quantitative compositlonal analysis of optically tMck SOW In motlon Is demonstrated by urbrg trandent Infrared emlsslon spectroocopy (TIRES). TIRES greatiy reduces the self-absorptkn that nonndly degrades comrenUona1 emlsskn spectra so that they dosdy resembb Msckbody spectra. Quantltathre composltlonal analyses of poly[( methyl methacrylate)-co -(butyl methacrylate)] and poly[ethylenaco-(vlnyl acetate)] with standard errors of predlctlon under 1 % were achleved with only a few seconds of data acqulsition uslng prlnclpal compomtt regresgkn. Use of a hotgas j e t in place of a laser In the TIRES technique allows study of materials that do not absorb strongly at common laser wavelengths whlle reducing cost and complexlty.